Collect as a Set certain values from Document in Update?

Question

Morning,

When trying to update a Document in MongoDB I'm trying to collect certain specified fields as a set, without non repeated items, and was wondering if this is achievable within the update clause in updateMany, I was trying with $addToSet but no luck so far.

I'm trying to do as follows:

    getCollection(...).updateMany(
            and(neq("sample_field", "SAMPLE")),
            ..., // Replace "array" also including "field_a" and "field_b" without having repated elements.
            new UpdateOptions().upsert(true)
    );

Having as input:

{"_id": 1, "field_a": "a", "field_b": "b", "field_c": "c", "array": ["c"]}
{"_id": 2, "field_a": "b", "field_b": "b", "field_c": "c", "array": ["c"]}

After running the update (including field_a and field_b in array) the output should be:

{"_id": 1, "field_a": "a", "field_b": "b", "field_c": "c", "array": ["a", "b", "c"]}
{"_id": 2, "field_a": "b", "field_b": "b", "field_c": "c", "array": ["b", "c"]}

Thanks in advance!